The present invention relates generally to underground bore location systems.
Those of ordinary skill in the art should recognize that the term “horizontal bore” refers to the excavation of a hole, typically for utilities, through the ground and to the excavated hole itself. The present invention relates to systems and methods for locating such bores, but also to such systems and methods for locating existing buried utilities, whether such existing utilities were initially installed by boring or trenching techniques. Accordingly, unless otherwise indicated, the term “bore” as used herein refers to new bores and to existing buried utilities or similar lines.
Boring location systems are utilized in a variety of circumstances. For example, in horizontal boring systems as are typically used for installing utilities, it is desirable to maintain a directional boring head in a desired boring path and to avoid known obstacles such as existing utilities. Accordingly, systems are known to trace existing utilities from an above-ground position.
The boring head, which may include a boring probe behind a drill head, is underground and is therefore not visible to the operator. Accordingly, the boring probe may be configured to transmit signals from the bore that provide location information to an above-ground operator. One system that is configured to determine whether an underground boring probe is laterally offset from its intended horizontal path is described in U.S. Pat. No. 4,881,083, the entire disclosure of which is incorporated herein by reference. This information is used, in turn, to maintain the boring head in its desired path. Typically, however, an above-ground receiver must be disposed at a known location relative to the boring head with respect to the head's desired path of travel in order to properly read certain location information. For example, assume that a boring head is to the right of its desired path and that an above-ground receiver is disposed along the path in an attempt to receive location information from which to determine whether the boring head should turn to the right or to the left to regain or maintain its path. Using one conventional receiver, the operator must know whether the boring head is ahead of or behind the above-ground receiver with respect to the desired path.